1. Field of the Invention
The present invention relates to a device and method of swapping optical labels and reproducing an optical payload, and an optical switching device using the device, and more particularly, to an optical label swapper and payload reproducer for switching optical burst signals in a network that employs an optical burst switch, and an optical burst switching device using the same.
This work was supported by the IT R&D program of MIC/IITA [2006-S-059-01, ASON based Metro Photonic Cross-Connect Technology]
2. Description of the Related Art
An existing optical transmission system employs an electrical switch when a switching operation is performed with respect to optical signals. However, an optical-electrical-optical (O/E/O) type network node, at which all the information at each node is opto-electrically converted and electrically processed, operates as a bottleneck of electrical processing of the information. In addition, the costs for electrically processing the information increase proportionally to an increase in the transmission capacity.
However, when express traffic is not converted into an electrical signal and passed as an optical signal type, and only add/drop is electro-optically converted and opto-electrically converted, at the node, the costs for the system are reduced, and the structure can be simplified.
In order to solve the problem, an optical burst switching system in which a transmitted optical signal is not converted into an electrical signal but directly processed as the optical signal is used.
FIG. 1 illustrates a structure of an existing optical burst switching network. A network that employs an optical burst switching technique as shown in FIG. 1 includes a departure node which is disposed at a network edge, a destination node in which a receiving unit is disposed, and a relay node through which an optical burst signal passes between departure and destination.
In the optical burst switching system, packet signals such as an input IP and the like are gathered at a network edge. A burst signal having a length greater than a predetermined length is generated and included in payloads. On the other hand, information on a moving direction of the payloads is included in the label. The optical burst signal includes the payloads and the labels.
The optical label is generated at the departure node and transmitted to the relay node. At the relay node, path information of the payload signals is recognized, and the payloads are switched by opto-electrically converting only label signals. In the switched payload signal, label information is updated and transmitted to the next node. This function is referred to as a label swapping function.
While the payload signals proceed along the transmission path, the quality of the signals may deteriorate. Thus, optical reproduction operation is performed. In order to prevent collision between wavelengths, wavelength-conversion may be performed, and availability of network resources increases.
A method that employs a time division multiplexing technique, a method that employs a code division multiplexing technique, and a method that employs a frequency division multiplexing technique (sub carrier wave) have been used as a method of transmitting labels. In the code division multiplexing technique, since a label swapping operation is performed by allocating different codes to the labels, a complicated encoder and decoder are needed.
In the frequency division multiplexing technique, that is, in a label swapping technique performed by allocating a separate sub carrier wave signal to the label, a separate frequency band is occupied, and therefore, frequency efficiency decreases. As the transmission speed increases, the frequency of the sub carrier wave increases, and thus is more influenced by a chromatic dispersion of an optical fiber.
On the contrary, in the time division multiplexing technique, since labels and payloads are transmitted by separating time regions of the labels and the payloads from each other, frequency efficiency is improved. There is an advantage in that the time division transmission technique which is a developed technology is used.
In the past, a technique that employs an all-optical label swapper as a relay node was known as a label swapping method based on a time division multiplexing technique. In this technique, an optical interferometer, which is constructed using a semiconductor optical amplifier, is used. A label swapping operation is performed by using a mutual phase modulation phenomenon generated in the semiconductor optical amplifier.
However, since a non-linear phenomenon in the semiconductor optical amplifier is used, the efficiency is low. The label swapping performance is seriously influenced by a polarization state, an optical power, a wavelength, and the type of an input light signal.